Active stylus and capacitive position detection system

ABSTRACT

An elongated stylus is configured to be capacitively coupled with a sensor array providing a plurality of electrodes to indicate a position on the sensor array. The stylus includes a housing having an end in an elongated direction of the housing, a conductive tip disposed at least partially extended from the end of the housing, an electrode disposed around the conductive tip and configured to at least partially expose the conductive tip, and a signal transmit drive circuit configured to provide a signal. Control is performed to form an electrical connection between the electrode and a ground and an electrical connection between the electrode and the signal transmit drive circuit when the elongated stylus is activated for capacitive coupling with the sensor array.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/896,950, filed Feb. 14, 2018, which is a continuation of U.S. patentapplication Ser. No. 15/866,033, filed Jan. 9, 2018, which is acontinuation of U.S. patent application Ser. No. 14/979,090, filed Dec.22, 2015, which is a continuation of U.S. patent application Ser. No.14/095,930, filed Dec. 3, 2013, now U.S. Pat. No. 9,218,073, issued Dec.22, 2015, which is a continuation of U.S. patent application Ser. No.13/431,425 filed Mar. 27, 2012, now U.S. Pat. No. 8,878,823, issued onNov. 4, 2014, which claims the benefit of U.S. Provisional PatentApplication No. 61/512,324, filed Jul. 27, 2011, all of the contents ofwhich are hereby incorporated by reference.

BACKGROUND Technical Field

This disclosure relates to the field of user interface devices and, inparticular, to capacitive sensor devices.

Description of the Related Art

The use of a stylus with a touch screen interface is well established.Touch screen designs have incorporated many different technologiesincluding resistive, capacitive, inductive, and radio frequency sensingarrays. Resistive touch screens, for example, are passive devices wellsuited for use with a passive stylus. The original PalmPilots® devicesfrom the mid-1990s were one of the first successful commercial devicesto utilize a resistive touch screen designed for use with a stylus andhelped to popularize that technology. Although resistive touch screenscan sense the input from nearly any object, multi-touch is generally notsupported. An example of a multi-touch application may be applying twoor more fingers to the touch screen. Another example may be inputting asignature, which may include simultaneous palm and stylus input signals.Due to these and other numerous disadvantages, capacitive touch screensare increasingly replacing resistive touch screens in the consumermarketplace.

Various capacitive stylus approaches have been implemented for use withtouch screens and are found in many consumer applications such aspoint-of-sale terminals (e.g., the signature pad used for credit cardtransactions in retail stores) and other public uses. However, any typeof capacitive stylus can be affected by the shadow effect which occursto some degree at any non-perpendicular angle between the stylus andsensing area.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example, and not oflimitation, in the figures of the accompanying drawings in which:

FIG. 1 is a block diagram illustrating one embodiment of an electronicsystem having a processing device for detecting a presence of a touchobject and a stylus.

FIG. 2 is a block diagram illustrating one embodiment of a systemincluding a capacitive sense array, a stylus, and a processing devicethat converts measured capacitances to touch coordinates.

FIG. 3A is a block diagram illustrating one embodiment of a systemincluding the sense array and a touch screen controller that convertsmeasured capacitances to touch coordinates.

FIG. 3B is a block diagram illustrating one embodiment of a systemincluding the sense array, a stylus, and the touch screen controllerthat converts measured capacitances to touch coordinates.

FIG. 4A is cross-sectional diagram illustrating an embodiment of thestylus tip.

FIG. 4B is cross-sectional diagram illustrating another embodiment ofthe stylus tip.

FIG. 5 is a schematic block diagram illustrating a cross-sectional viewof a stylus having a dynamically switched tip shield.

FIG. 6 is a schematic flow chart diagram illustrating one embodiment ofa method for dynamic shield switching of the tip shield.

FIG. 7 is a schematic block diagram graphically illustrating shadoweffect correction.

FIG. 8 is a perspective view diagram illustrating one embodiment of astylus having a force sensor.

FIG. 9a is a block diagram illustrating one embodiment of a plungercoupled with the stylus tip.

FIG. 9b is a block diagram illustrating another embodiment of a forcesensor utilizing a deformable actuator.

FIG. 9c is a block diagram illustrating one embodiment of a deformableactuator directly in contact with both the stylus tip and sensorsubstrate.

FIG. 9d is a block diagram illustrating the operation of a deformablepartially conductive actuator.

FIG. 9e is a block diagram illustrating one embodiment of an opticalsubstrate sensor for use with the deformable actuator.

FIG. 9f is a block diagram illustrating one embodiment of a capacitivesubstrate sensor for use with the deformable actuator.

DETAILED DESCRIPTION

Apparatuses and methods of a dynamically switched tip shield for astylus are described. The apparatus, in one embodiment, includes anelongated stylus housing having an end, a conductive tip disposed atleast partially inside the stylus housing and extending from the end, aforce sensor coupled to the conductive tip and configured to detectcontact between the conductive tip and an object, a tip shield coupledwith the stylus housing and extending from the end, and a switch coupledto the tip shield and the conductive tip.

In the following description, for purposes of explanation, numerousspecific details are set forth in order to provide a thoroughunderstanding of the present invention. It will be evident, however, toone skilled in the art that the present invention may be practicedwithout these specific details. In other instances, well-known circuits,structures, and techniques are not shown in detail, but rather in ablock diagram in order to avoid unnecessarily obscuring an understandingof this description.

Reference in the description to “one embodiment” or “an embodiment”means that a particular feature, structure, or characteristic describedin connection with the embodiment is included in at least one embodimentof the invention. The phrase “in one embodiment” located in variousplaces in this description does not necessarily refer to the sameembodiment.

FIG. 1 is a block diagram illustrating one embodiment of an electronicsystem 100 having a processing device 110 for detecting a presence of atouch object 140 and a stylus 130. The electronic system 100 includesthe processing device 110, a capacitive sense array 125, a stylus 130, ahost processor 150, an embedded controller 160, and non-capacitive senseelements 170. In the depicted embodiment, the electronic system 100includes the capacitive sense array 125 coupled to the processing device110 via a bus 122. The capacitive sense array 125 may include amulti-dimension capacitive sense array. The multi-dimension sense arrayincludes multiple sense elements, organized as rows and columns. Inanother embodiment, the capacitive sense array 125 operates as anall-points-addressable (“APA”) mutual capacitive sense array. In anotherembodiment, the capacitive sense array 125 operates as a coupled-chargereceiver. Alternatively, other configurations of capacitive sense arraysmay be used. In one embodiment, the capacitive sense array 125 may beincluded in an ITO panel or a touch screen panel.

The processing device 110 may detect and track the active stylus 130 andthe touch object 140 individually on the capacitive sense array 125. Inone embodiment, the processing device 110 can detect and track both theactive stylus 130 and the touch object 140 concurrently on thecapacitive sense array 125. In one embodiment, the active stylus 130 isconfigured to operate as the timing “master,” and the processing device110 adjusts the timing of the capacitive sense array 125 to match thatof the active stylus 130 when the active stylus 130 is in use.

In one embodiment, the capacitive sense array 125 capacitively coupleswith the active stylus 130, as opposed to conventional inductive stylusapplications. It should also be noted that the same assembly used forthe capacitive sense array 125, which is configured to detect touchobjects 140, is also used to detect and track the active stylus 130without an additional PCB layer for inductively tracking the activestylus 130 as done conventionally.

In the depicted embodiment, the processing device 110 includes analogand/or digital general purpose input/output (“GPIO”) ports 107. GPIOports 107 may be programmable. GPIO ports 107 may be coupled to aProgrammable Interconnect and Logic (“PIL”), which acts as aninterconnect between GPIO ports 107 and a digital block array of theprocessing device 110 (not shown). The digital block array may beconfigured to implement a variety of digital logic circuits (e.g., DACs,digital filters, or digital control systems) using, in one embodiment,configurable user modules (“UMs”).

The digital block array may be coupled to a system bus. The processingdevice 110 may also include memory, such as random access memory (“RAM”)105 and program flash 104. RAM 105 may be static RAM (“SRAM”), andprogram flash 104 may be a non-volatile storage, which may be used tostore firmware (e.g., control algorithms executable by the processingcore 102 to implement operations described herein). The processingdevice 110 may also include a memory controller unit (“MCU”) 103 coupledto memory and the processing core 102.

The processing device 110 may also include an analog block array (notshown). The analog block array is also coupled to the system bus. Theanalog block array also may be configured to implement a variety ofanalog circuits (e.g., ADCs or analog filters) using, in one embodiment,configurable UMs. The analog block array may also be coupled to the GPIO107.

As illustrated, the capacitance sensor 101 may be integrated into theprocessing device 110. The capacitance sensor 101 may include analog I/Ofor coupling to an external component, such as a touch-sensor pad (notshown), a capacitive sense array 125, a touch-sensor slider (not shown),touch-sensor buttons (not shown), and/or other devices.

The capacitance sensor 101 may be configured to measure capacitanceusing mutual capacitance sensing techniques, self-capacitance sensingtechnique, charge coupling techniques or the like. In one embodiment,the capacitance sensor 101 operates using a charge accumulation circuit,a capacitance modulation circuit, or other capacitance sensing methodsknown by those of skill in the art.

In an embodiment, the capacitance sensor 101 is of the Cypress TMA-4xxfamily of touch screen controllers. Alternatively, other capacitancesensors may be used. The mutual capacitive sense arrays, or touchscreens, as described herein, may include a transparent, conductivesense array disposed on, in, or under either a visual display itself(e.g., LCD monitor), or a transparent substrate in front of the display.

In an embodiment, the TX and RX electrodes are configured in rows andcolumns, respectively (see FIG. 2). It should be noted that the rows andcolumns of electrodes can be configured as TX or RX electrodes by thecapacitance sensor 101 in any chosen combination. In one embodiment, theTX and RX electrodes of the sense array 200 of FIG. 2 are configured tooperate as a TX and RX electrodes of a mutual capacitive sense array ina first mode to detect touch objects, and to operate as electrodes of acoupled-charge receiver in a second mode to detect a stylus 130 on thesame electrodes of the sense array.

The stylus 130, which generates a stylus TX signal when activated, isused to couple charge to the capacitive sense array, instead ofmeasuring a mutual capacitance at an intersection of an RX electrode anda TX electrode (a sense element) as done during mutual capacitancesensing. The capacitance sensor 101, in one embodiment, does not usemutual capacitance or self-capacitance sensing to measure capacitancesof the sense elements when performing a stylus scan. Rather, thecapacitance sensor 101 may measure a charge that is capacitively coupledbetween the sense array 200 and the stylus as described herein.

The capacitance associated with the intersection between a TX electrodeand an RX electrode can be sensed by selecting every availablecombination of TX electrode and RX electrode. When a touch object, suchas a finger or stylus, approaches the capacitive sense array 125, theobject causes a decrease in capacitance affecting some of theelectrodes.

In another embodiment, the presence of the finger increases the couplingcapacitance between the two electrodes. Thus, the location of the fingeron the capacitive sense array 125 can be determined by identifying boththe RX electrode having a decreased coupling capacitance between the RXelectrode and the TX electrode to which the TX signal was applied at thetime the decreased capacitance was measured on the RX electrode.Therefore, by sequentially determining the capacitances associated withthe intersection of electrodes, the locations of one or more inputs canbe determined.

It should be noted that the process can calibrate the sense elements(intersections of RX and TX electrodes) by determining baselines for thesense elements. It should also be noted that interpolation may be usedto detect finger position at better resolutions than the row/columnpitch, as would be appreciated by one of ordinary skill in the arthaving the benefit of this disclosure. In addition, various types ofcentroid algorithms may be used to detect the center of the touch, aswould be appreciated by one of ordinary skill in the art having thebenefit of this disclosure.

In one embodiment, the electronic system 100 includes a touch sensor padcoupled to the processing device 110 via a bus. The touch sensor pad mayinclude a multi-dimension capacitive sense array. The multi-dimensionsense array includes multiple sense elements, organized as rows andcolumns. In another embodiment, the touch sensor pad is an APA mutualcapacitive sense array. In another embodiment, the touch sensor padoperates as a coupled-charge receiver.

In an embodiment, the electronic system 100 may also includenon-capacitive sense elements 170 coupled to the processing device 110via bus 171 and GPIO port 107. The non-capacitive sense elements 170 mayinclude buttons, light emitting diodes (“LEDs”), and other userinterface devices, such as a mouse, a keyboard, or other functional keysthat do not use capacitance sensing. In one embodiment, buses 151, 122,and 171 are embodied in a single bus. Alternatively, these buses may beconfigured into any combination of one or more separate buses.

The processing device 110 may include internal oscillator/clocks 106 anda communication block (“COM”) 108. In another embodiment, the processingdevice 110 includes a spread spectrum clock (not shown). Theoscillator/clocks block 106 provides clock signals to one or more of thecomponents of the processing device 110.

The communication block 108 may be used to communicate with an externalcomponent, such as a host processor 150, via host interface (“I/F”) line151. Alternatively, the processing device 110 may also be coupled toembedded controller 160 to communicate with the external components,such as host processor 150. In one embodiment, the processing device 110is configured to communicate with the embedded controller 160 or thehost processor 150 to send and/or receive data.

The processing device 110 may reside on a common carrier substrate suchas, for example, an integrated circuit (“IC”) die substrate, amulti-chip module substrate, or the like. Alternatively, the componentsof the processing device 110 may be one or more separate integratedcircuits and/or discrete components. In one exemplary embodiment,processing device 110 is the Programmable System on a Chip (PSoC®)processing device, developed by Cypress Semiconductor Corporation, SanJose, Calif. Alternatively, the processing device 110 may be one or moreother processing devices known by those of ordinary skill in the art,such as a microprocessor or central processing unit, a controller,special-purpose processor, digital signal processor (“DSP”), anapplication specific integrated circuit (“ASIC”), a field programmablegate array (“FPGA”), or the like.

It should also be noted that the embodiments described herein are notlimited to having a configuration of a processing device coupled to ahost, but may include a system that measures the capacitance on thesensing device and sends the raw data to a host computer where it isanalyzed by an application. In effect, the processing that is done byprocessing device 110 may also be done in the host 150.

The capacitance sensor 101 may be integrated into the IC of theprocessing device 110, or alternatively, in a separate IC.Alternatively, descriptions of the capacitance sensor 101 may begenerated and compiled for incorporation into other integrated circuits.For example, behavioral level code describing the capacitance sensor101, or portions thereof, may be generated using a hardware descriptivelanguage, such as VHDL or Verilog, and stored to a machine-accessiblemedium (e.g., CD-ROM, hard disk, floppy disk, etc.). Furthermore, thebehavioral level code can be compiled into register transfer level(“RTL”) code, a netlist, or even a circuit layout and stored to amachine-accessible medium. The behavioral level code, the RTL code, thenetlist, and the circuit layout may represent various levels ofabstraction to describe the capacitance sensor 101.

It should be noted that the components of the electronic system 100 mayinclude all the components described above. Alternatively, theelectronic system 100 may include some of the components describedabove.

In one embodiment, the electronic system 100 is used in a tabletcomputer. Alternatively, the electronic system 100 may be used in otherapplications, such as a notebook computer, a mobile handset, a personaldata assistant (“PDA”), a keyboard, a television, a remote control, amonitor, a handheld multi-media device, a handheld media (audio and/orvideo) player, a handheld gaming device, a signature input device forpoint of sale transactions, an eBook reader, a global position system(“GPS”) or a control panel.

The embodiments described herein are not limited to touch screens ortouch-sensor pads for notebook implementations, but can be used in othercapacitive sensing implementations, for example, the sensing device maybe a touch-sensor slider (not shown) or touch-sensor buttons (e.g.,capacitance sensing buttons). In one embodiment, these sensing devicesinclude one or more capacitive sensors. The operations described hereinare not limited to notebook pointer operations, but can include otheroperations, such as lighting control (dimmer), volume control, graphicequalizer control, speed control, or other control operations requiringgradual or discrete adjustments. It should also be noted that theseembodiments of capacitive sensing implementations may be used inconjunction with non-capacitive sensing elements, including but notlimited to pick buttons, sliders (e.g., display brightness andcontrast), scroll-wheels, multi-media control (e.g., volume, trackadvance, etc.) handwriting recognition, and numeric keypad operation.

FIG. 2 is a block diagram illustrating one embodiment of a systemincluding a capacitive sense array, a stylus, and a processing devicethat converts measured capacitances to touch coordinates. The processingdevice 110 includes a processing core 102, a TX driver circuit 212, anRX sense circuit 214, a multiplexer 218, and a force sensor demodulator216. In an embodiment, the processing core 102 is similar to thecapacitance sensor 101 described above. The sense array 200 includesmultiple lines that can be configured as TX lines or RX lines. Forexample, in one mode, the TX drive circuit 212 drives a TX signal on afirst set of TX lines, and the RX sense circuit 214 measures signals ona second set of RX lines. In another mode, the TX lines are RX lines andthe RX sense circuit 214 is configured to measure signals on two sets ofRX lines (as illustrated in FIG. 2). These sets of RX lines can beconsidered as separate receive channels for stylus signal sensing. Itshould be noted that TX and RX lines are also referred to as TX and RXelectrodes. The multiplexer 218 can be used to connect the TX lines orthe RX lines to the TX drive circuit 212 or the RX sense circuit 214based on whether the lines are being used as RX lines or TX lines.

In one embodiment, during normal finger scanning, a passive object(e.g., a finger or other conductive object) touches the sense array 200at contact point (not illustrated in FIG. 2). The TX drive circuit 212drives the TX lines with a TX signal. The RX sense circuit 214 measuresthe RX signals on RX lines. In an embodiment, the processing core 102determines the location of contact point based on the mappingtechniques, as would be appreciated by one of ordinary skill in the arthaving the benefit of this disclosure.

Alternatively, other techniques may be used to determine the contactpoint. The TX lines and RX lines are multiplexed by multiplexor 330. Theprocessing core 102 provides the TX signal on the TX lines (rows) andmeasures the capacitance coupling on the RX lines (columns). In anembodiment, the TX and RX lines are orthogonal and may be usedinterchangeably (e.g., transmitting on columns and receiving on rows).In an embodiment, the TX drive circuit 212 transmits the TX signalthrough a high impedance ITO panel (TX lines), thus limiting the upperfrequency limit and speed of the system. The total scan time may also bedependent upon the number of TX lines and RX lines in the sense array200. For example, the TX drive circuit 212 provides a TX signal on a TXline and simultaneously reads the capacitively coupled RX signal on anRX line, according to one embodiment. In another embodiment, the RXlines are multiplexed in two or more scans.

In one embodiment, during stylus scanning, the stylus TX drive circuit222 of stylus 130 provides a TX signal 227 directly to contact point 228on the sense array 200, thus eliminating the need to dedicate the secondset of RX lines (previously TX in finger scanning) to transmitting a TXsignal from the TX drive circuit 212. As such, the RX sense circuit 214measures the RX signal on both the first set of RX lines (rows) and asecond set of RX lines (columns) of sense array 200. This may result infaster position tracking because the TX signal no longer passes throughthe high impedance ITO lines, thus reducing the scan time to the totalRX measurement. The active stylus 130 includes the TX drive circuit 222,a microcontroller (MCU) 224, and a force sensor 226. In one embodiment,the processing core 102 performs a normal scan of the sense array 200during RX sensing of TX signal from the TX drive circuit 212 (describedabove), and a stylus scan of the sense array 200 during RX sensing ofthe stylus TX signal 227.

The stylus 130 includes the TX drive circuit 222 (also referred to as atip driver), and an MCU 224. The host 150 of FIG. 1 generates a TXsignal and transmits the TX signal to the stylus 130. The signal can betransmitted by radio, inductively, optically, or other methods ofcommunication. A receiver (not shown) receives the TX signal via anantenna and the receiver can send the TX signal to the MCU 224 to betransmitted by the stylus tip via the TX drive circuit 222.Alternatively, other frequency and other communication mediums may beused, as would be appreciated by one of ordinary skill in the art havingthe benefit of this disclosure.

In an embodiment, the stylus 130 is powered by battery voltage. Thebattery voltage may be provided by battery cells (e.g., 1.5V AAA cells).A booster (not illustrated) may boost the battery voltage delivered to atip driver (e.g., a TX driver circuit 222), allowing the tip driver toamplify the TX signal to a higher voltage (e.g., 10V-20V). A highvoltage stylus TX signal may enable the host 150 to detect the stylus130 when it is “hovering,” or in close proximity to the sense array 200,but not physically touching an overlay disposed over the sense array. Ahigh voltage stylus TX signal may also provide for faster and morerobust detection by the host 150.

For the stylus scan, the processing core 102 measures a charge beingcapacitively coupled to the row and column electrodes of the sense arrayfrom the stylus. To further illustrate, a mutual capacitance scan usesboth a TX and RX signal to track an object. As described above, this istypically done by scanning the RX lines for the driven TX line in asuccessive fashion by the processing core 102. In an array of N rows (TXsignal) and M columns (RX signal), a complete scan would perform N×Mtotal scans if one RX line is sensed at a time. For example,transmitting a TX signal (“TX'ing”) on row 1, and receiving a receivesignal (“RX'ing”) on columns 1-M, followed by TX'ing on row 2 and RX'ingon columns 1-M, and so on in sequential fashion. Alternatively, more RXlines can be sensed at a time. In one embodiment, four or eight RX linesare sensed at a time, but in other embodiments, all RX lines may besense simultaneously or sequentially.

With multiple RX channels to sense more than one RX line at the sametime, the complete scan would be (N*M)/(#RX channels). In contrast, astylus scan may not use a TX signal by the TX drive circuit 212 and acomplete scan would perform a single RX signal measurement on each rowand column, or N+M scans, thus resulting in a significantly reducedstylus scanning time for the entire sense array as compared with mutualcapacitance scanning time for the entire sense array. Like above,multiple RX channels can be used to sense multiple RX lines at the sametime. In this case, the complete scan would be (N+M)/(#RX channels).

In the depicted embodiment, the TX driver circuit 212 generates a stylusTX signal 227 from the tip of the active stylus 130 into the touchscreen. The processing core 102 senses this signal and resolves this tobe the point of the active stylus 130. The TX signal 227 of the stylusmay, in one embodiment, be synchronized to the host. Synchronizationbetween the processing core 102 sensing and the signal generated by theactive stylus 130 is used in some active stylus configurations. In theun-tethered active stylus, this synchronization is done wirelessly. Thehost side (e.g., tablet side) antenna transmits a synchronization signalthat is received by an antenna inside the active stylus 130. In oneembodiment, the un-tethered active stylus solution uses magneticcoupling between the host and the stylus for signal transmitting. Inthis embodiment, the antenna design provides a uniform magnetic fieldacross the display surface.

As described above, a passive stylus may be used as a touch object tointerface with the various touch screens described above. In contrast topassive styluses, an active stylus 130 provides the transmit signal 227(TX signal). This signal 227 may be provided to the active stylus 130 bythe processing core 102 as part of the synchronization. The activestylus 130 capacitively couples the stylus TX signal 227 to the sensearray 200.

In an embodiment, the stylus signal amplitude, frequency, phase, etc.,may be the same or similar to that which is utilized for finger sensingby the processing core 102. Alternatively, the stylus TX signal may bedifferent than the TX signal from the TX drive circuit 212, inamplitude, frequency, and phase. In another embodiment, the stylus TXsignal may have a different code for code modulation than a code used inthe TX signal from the TX drive circuit 212. In an exemplary embodiment,the stylus TX signal 227 has greater amplitude than the finger sensingTX signal from the TX drive circuit 212. For example, in one exemplaryembodiment, the stylus TX signal 227 ranges from approximately 20V-50V,as compared with the approximately 5V-10V typically provided by theprocessing core 102. Alternatively, other voltages may be used, as wouldbe appreciated by one of ordinary skill in the art. The higher stylus TXvoltage couples more charge to the sense array 200 more quickly, thusreducing the amount of time used to sense each row and column of thesense array 200. Other embodiments may incorporate higher voltages onthe sense array TX lines to obtain similar time efficiency improvementsfor finger sensing.

In an embodiment, the active stylus 130 applies a higher frequency onthe stylus TX signal 227 than the TX signal frequency from TX drivecircuit 212 to achieve a reduced sensing time. Charge may becapacitively coupled from the active stylus 130 to the sense array 200during the rising and falling edges of the stylus TX signal 227. Thus, ahigher TX frequency provides a greater number of rising and fallingedges over a given period of time, resulting in greater charge coupling.

The practical upper limit of the TX frequency in finger sensing mode(e.g., TX signal on sense array 200 for finger sensing) is dependentupon the resistor-capacitor (“RC”) time constant of the panel'sindividual sense elements and interconnect (not shown). This istypically due to high impedance materials (e.g., ITO) used in thefabrication of the sense array 200.

A high-impedance sense array (e.g., sense array 200) may result in ahigh time constant and resulting signal attenuation of the rows (TXlines) and columns (RX lines) of sense elements, which may limit themaximum sensing frequency. When using an active stylus to transmit thestylus TX signal 227 directly to a contact point 228 on sense array 200,the stylus TX signal 227 does not pass through the high impedance path,and therefore the maximum operating frequency for the stylus TX signal227 can be increased. For example, the time constant of the RX traces(both rows and columns) may be used to determine an upper frequencylimit, but this will typically be at least double the upper frequencylimit used in finger sensing. Typically the impedance is half of theimpedance when performing mutual capacitance scanning, since the row'simpedance is eliminated and the column's impedance remains (or viceversa). It should be noted that both finger sensing and stylus sensinguse frequency selection where the operation period should be smallerthan the panel's time constant; so, restrictions for the operationfrequency selection are approximately the same for finger and stylussensing.

Although the RX lines (electrodes) appear as lines in FIG. 2, theselines may represent bars or elongated rectangles or other tessellatedshapes such as diamonds, rhomboids, and chevrons. Alternatively, otheruseable shapes may be used, as would be appreciated by one of ordinaryskill in the art having the benefit of this disclosure.

FIG. 3A is a block diagram illustrating one embodiment of a system 300including the sense array 301 and a touch screen controller 305 thatconverts measured capacitances to touch coordinates. In an embodiment,the touch screen controller 305 is similar to the capacitance sensor 301described above. In another embodiment, the touch screen controller 305is the processing device 310. The sense array 301 includes TX lines 335and RX lines 340. The touch screen controller 305 includes a TX drivecircuit 310, an RX sense circuit 320, and a multiplexor 330.

In an embodiment, a passive object (e.g., a finger or other conductiveobject) touches the sense array 301 at contact point 345. The TX drivecircuit 310 drives the TX lines 335 with TX signal 332. The RX sensecircuit 320 measures the RX signal 334 on RX lines 340. In anembodiment, the touch screen controller 305 determines the location ofcontact point 345 based on the mapping techniques described above inconjunction with FIGS. 1-2. The TX lines 335 and RX lines 340 aremultiplexed by multiplexor 330. The touch screen controller 305 providesthe TX signal 332 on the TX lines 335 (rows) and measures thecapacitance coupling on the RX lines 340 (columns).

In an embodiment, the TX and RX lines 335, 340 are orthogonal and may beused interchangeably (e.g., transmitting on columns and receiving onrows). In an embodiment, the TX drive circuit 310 transmits the TXsignal 332 through a high impedance ITO panel (TX lines 335), thuslimiting the upper frequency limit and speed of the system. The totalscan time may also be dependent upon the number of TX lines 335 and RXlines 340 in the sense array 301. For example, the TX drive circuit 310provides a TX signal 332 on each TX line 335 and simultaneously readsthe capacitively coupled RX signal 334 on each RX line 340, according toone embodiment. In another embodiment, the RX lines 340 are multiplexedin two or more scans, as described in conjunction with FIG. 3B.

FIG. 3B is a block diagram illustrating one embodiment of a system 300including the sense array 301, a stylus 380, and the touch screencontroller 305 that converts measured capacitances to touch coordinates.The sense array 301 includes RX lines 340 and 360. The RX lines 360 arethe same as TX lines 335 in FIG. 3A, but used as a receive channel insystem 300 as further described below for stylus signal sensing. Thetouch screen controller 305 includes the TX drive circuit 310, the RXsense circuit 320, and the multiplexor 330. The stylus 380 includes a TXdrive circuit 385 and a stylus tip 388.

In an embodiment, the stylus TX drive circuit 385 of stylus 380 providesa TX signal 377 directly to contact point 395 on sense array 301, thuseliminating the need to dedicate the RX 360 lines (previously TX 335 inFIG. 3A) to transmitting a TX signal from the TX drive circuit 310. Assuch, the RX sense circuit 320 measures the RX signal 334 on both therows (RX lines 360) and columns (RX lines 340) of sense array 301. Thisresults in faster position tracking because the TX signal no longerpasses through the high impedance ITO lines, thus reducing the scan timeto the total RX measurement. In one embodiment, the touch screencontroller 305 performs a normal scan of the sense array 301 during RXsensing of the TX signal from the TX drive circuit 310 (illustrated inFIG. 3A), and a stylus scan of the sense array 301 during RX sensing ofthe stylus TX signal 377.

For the stylus scan, the touch screen controller 305 measures a chargebeing capacitively coupled to the row and column electrodes of the sensearray from the stylus. To further illustrate, a mutual capacitance scanuses both a TX and RX signal 332, 334 to track an object. As describedabove, this is typically done by scanning the RX lines 340 for eachdriven TX line 335 in a successive fashion by the touch screencontroller 305. In an array of N rows (TX signal) and M columns (RXsignal), a complete scan would require N×M total scans if one RX line issensed at a time. For example, transmitting a TX signal (“TX'ing”) onrow 1, and receiving a receive signal (“RX'ing”) on columns 1-M,followed by TX'ing on row 2 and RX'ing on columns 1-M, and so on insequential fashion.

Alternatively, more RX lines can be sensed at a time. In one embodiment,four or eight RX lines are sensed at a time, but in other embodiments,all RX lines may be sensed simultaneously or sequentially. With multipleRX channels to sense more than one RX line at the same time, thecomplete scan would be (N*M)/(#RX channels). In contrast, a stylus scandoes not require a TX signal by the TX drive circuit 310 and a completescan would only require a single RX signal measurement on each row andcolumn, or N+M scans, thus resulting in a significantly reduced stylusscanning time for the entire sense array as compared with mutualcapacitance scanning time for the entire sense array. Like above,multiple RX channels can be used to sense multiple RX lines at the sametime. In this case, the complete scan would be (N+M)/(#RX channels).

It should be noted that the embodiments described herein may use thesame electrodes (e.g., ITO panel lines), for the RX function for thestylus sensing as those used for the TX function for the touch scanning.It should also be noted that both stylus and finger sensing operate atfrequencies which are not attenuated largely by the sensing device(e.g., ITO panel).

As described above, a passive stylus may be used as a touch object tointerface with the various touch screens described above. In contrast topassive styluses, an active stylus described herein provides thetransmit (“TX”) signal that is typically provided by the touch screencontroller 305 in finger sensing modes.

The stylus 380 capacitively couples the stylus TX signal 377 to thesense array 301. In an embodiment, the stylus signal amplitude,frequency, phase, etc., may be the same or similar to that which isutilized for finger sensing by the touch screen controller 305.Alternatively, the stylus TX signal may be different than the TX signalfrom the TX drive circuit 310, in amplitude, frequency, and phase. Inanother embodiment, the stylus TX signal may have a different code forcode modulation than a code used in the TX signal from the TX drivecircuit 310. In an exemplary embodiment, the stylus TX signal 377 has agreater amplitude than the finger sensing TX signal 332 from the TXdrive circuit 310. For example, in one exemplary embodiment, the stylusTX signal 377 ranges from approximately 20V-50V, as compared with theapproximately 5V-10V typically provided by the touch screen controller305.

Alternatively, other voltages may be used, as would be appreciated byone of ordinary skill in the art. The higher stylus TX voltage couplesmore charge to the MC array 301 more quickly, thus reducing the amountof time required to sense each row and column of the sense array 301.Other embodiments may incorporate higher voltages on the MC array TXline 335 to obtain similar time efficiency improvements for fingersensing.

In an embodiment, the stylus 380 applies a higher frequency on thestylus TX signal 377 than the TX signal 332 frequency from TX drivecircuit 310 to achieve a reduced sensing time. Charge may becapacitively coupled from the stylus 380 to the sense array 301 duringthe rising and falling edges of the stylus TX signal 377. Thus, a higherTX frequency provides a greater number of rising and falling edges overa given period of time, resulting in greater charge coupling. Thepractical upper limit of the TX frequency in finger sensing mode (e.g.,TX signal on sense array 301 for finger sensing) is dependent upon theresistor-capacitor (“RC”) time constant of the panel's individual senseelements and interconnect (not shown). This is typically due to highimpedance materials (e.g., ITO) used in the fabrication of the sensearray 301.

A high-impedance sense array 301 may result in a high time constant andresulting signal attenuation of the rows (TX lines 335) and columns (RXlines 340) of sensors, which may limit the maximum sensing frequency.When using an active stylus to transmit the stylus TX signal 377directly to a contact point on sense array 301, the stylus TX signal 377does not have to pass through all of the high impedance paths, andtherefore the maximum operating frequency for the stylus TX signal 377can be increased. For example, the time constant of the RX traces (bothrows and columns) may be used to determine an upper frequency limit, butthis will typically be is at least double the upper frequency limit usedin finger sensing. Typically the impedance is half to the impedance whenperforming mutual capacitance scanning, since the row's impedance iseliminated and the column's impedance remains (or vice versa). It shouldbe noted that both finger sensing and stylus sensing use frequencyselection where the operation period should be smaller than the panel'stime constant; so, restrictions for the operation frequency selectionare approximately the same for finger and stylus sensing.

In an embodiment, the frequency of the stylus TX signal 377 is differentthan the frequency of the finger sensing TX signal 332. By usingdifferent TX frequencies, the touch screen controller 305 candifferentiate between stylus TX signals and finger sensing TX signals.Alternatively, the touch screen controller 305 can differentiate thestylus TX signals from the TX drive circuit 310 TX signals 332 usingother techniques, as would be appreciated by those of ordinary skill inthe art with the benefit of this disclosure, such as detecting thedifference in signal characteristics (e.g., phase, frequency, amplitude,and code modulation).

Various embodiments described herein are applicable to any mutualcapacitance touch screen system using an untethered, or wireless activestylus configured to be capacitively coupled to the mutual capacitancearray, where the active stylus receives synchronization or timing datafrom the touch screen controller. For example, the stylus can generatethe stylus TX signals according to the synchronization or timing datareceived from the touch screen controller.

FIGS. 4A and 4B are cross-sectional diagrams illustrating embodiments ofthe stylus tip 388. The stylus tip 388 interacts with the sensor array301 to create an electric field depicted here by dashed lines. When thestylus tip 388 is in a substantially perpendicular orientation withregard to the sensor array 301, the electric field is substantiallysymmetric, as depicted. However, a user typically holds the stylus at anangle with respect to touchpad screen surface. The angle of the stylus,and subsequently the stylus tip, results in a substantially irregularelectric field also referred to as the shadow effect. This irregularelectric field causes the processing device 110 to incorrectly identifythe position of the stylus with reference to the sensor array 301.

FIG. 5 is a schematic block diagram illustrating a cross-sectional viewof a stylus 500 having a dynamically switched tip shield 502. In anembodiment, the tip shield 502 is a metal shield around the stylus tip504 that can reduce the shadow effect on a sensor array, and therebyimprove position accuracy. The tip shield 502 inhibits the electricfield generated at the sides 506 of the stylus tip 504 and decreasesstylus tip to ITO sense current.

The tip shield 502 extends from and is coupled with a stylus housing508. The tip shield 502, in one mode, has the same potential as thestylus housing 508. In other words, the tip shield 502, in one mode, isgrounded with the stylus housing. In another embodiment, the tip shield502 can be connected to any low impedance constant node, for example,power supply nets, voltage source, etc. Grounding or isolating the tipshield 502 from the stylus tip 504 shields the electric field generatedby the TX driver, as described above, and subsequently reduces theshadow effect of an unshielded stylus tip 504.

In another mode the tip shield 502 is electrically coupled to the stylustip 504 to improve hover mode, as described above with reference to FIG.5. The tip shield 502, in one embodiment, may be coupled to the stylustip 504 by way of a conductive path 510. A switch 512 a is disposedbetween the tip shield 502 and the stylus tip 504. A stylus controller514 is configured to control the switch 512 a in either a first closedmode or an open second mode. One example of a stylus controller 514suitable for use in the embodiment of FIG. 5 is described above withreference to PSoC 224 of FIG. 2. Alternatively, the controller 514comprises a switching circuit configured to transmit the TX potentialover multiple outputs, or in other words, the controller 514 isconfigured to selectively transmit the TX potential to the tip shield502 and/or the conductive stylus tip 504.

In the first mode, the switch 512 a is closed, thereby completing thepath 510 to the tip shield 502 and electrically coupling the tip shield502 with the stylus tip 504. In the first mode, the controller 514 sendsthe same TX potential to both the tip shield 502 and the stylus tip 504,thereby increasing hover sensitivity and hover distance. For clarity,the controller 514 of FIG. 5 represents the components of the stylus 130described above in FIG. 2.

In the second operating mode, the controller 514 instructs the switch512 a to open and electrically isolate the tip shield 502 from thestylus tip 504. In another embodiment, a second switch 512 b may connectthe tip shield 502 to device ground or any other constant voltagesource. In the second operating mode, the tip shield 502 shields anyelectric field that may occur at the sides 506 of the stylus tip 504,and thereby reduce shadow effects. The controller 514 instructs theswitch 512 a to open, in one embodiment, when the stylus tip 504 comesin contact with an object such as a touch screen. Upon contacting atouch screen, which subsequently moves the stylus tip 504 into thestylus housing 508, the controller 514 instructs the switch 512 a toenter an “open” state. The controller 514 includes, as is describedabove, a force sensor for detecting contact between the stylus tip 504and an object. The force sensor will be described in greater detailbelow with reference to FIGS. 8-9 f.

In an alternative embodiment, the tip shield 502 may not be electricallycoupled with the stylus tip 504, but rather receive the same TXpotential as the stylus tip 504 as determined by the controller 514. Inother words, the controller 504 is configured with a TX potential outputfor each of the tip shield 502 and the stylus tip 504. In anotherembodiment, the controller 514 is configured to determine when thestylus tip 504 is proximate an object such as the sensor array. Forexample, the controller 514 may be configured to measure proximity basedon an increase in the electrical field around the stylus tip 504, andelectrically isolate or ground the tip shield 502 when the strength ofthe electrical field is greater than a threshold value.

FIG. 6 is a schematic flow chart diagram illustrating one embodiment ofa method for dynamic shield switching of the tip shield. The method 600starts and the controller measures 602 the force sensor value 602.Measuring 602 the force sensor value, in one embodiment, refers todetermining a force value from a sensor. Examples of suitable sensorsinclude, but are not limited to, inductive, capacitive, resistive, forcesensing resistor, piezo, and optical sensors.

If the controller determines 604 that the force sensor is activated, thecontroller isolates 606 the tip shield and connects the tip shield toground or any other constant voltage source. In one embodiment,isolating 606 the tip shield comprises instructing the switch of FIG. 5to open. Alternatively, the controller may ground or isolate the tipshield by not sending the same TX potential to the tip shield. If theforce sensor is not activated 604, then the stylus is in hover mode andthe controller connects 608 the tip shield to the TX potential of thestylus tip to increase hover sensitivity and hover distance.

FIG. 7 is a schematic block diagram graphically illustrating shadoweffect correction 700. The processing device 305 of FIG. 3 may beconfigured to correct shadow effect by analyzing centroid data. Centroiddata refers to, in one embodiment, data that identifies the center of atouch from the stylus. When the stylus 502 is perpendicular to the ITOsensors 704, there is no shadow effect, and the ITO sensor directlyunder the stylus 702 indicates the center of the touch. However, whenthe stylus 702 is at a non-perpendicular angle to the ITO sensors 704, afourth ITO 706 sensor will detect the stylus 702 and cause the “center”of the touch to shift towards the new data point.

The controller 305, in one embodiment, is configured to correct for thecenter shift by subtracting the new data 706 from the neighborelectrode, or ITO sensor, and adding the value to the far electrode asdepicted. In an embodiment, when the stylus 702 is perpendicular, threeelectrodes will be active. If a fourth electrode is active, thisindicates to the controller 305 that the stylus is not perpendicular tothe surface of the sensor array, and the fourth sensor information maybe used to compensate for the shadow effect.

FIG. 8 is a perspective view diagram illustrating one embodiment of astylus 800 having a force sensor. FIG. 8 also depicts an exploded viewdiagram of one example of a force sensor integrated into the tip area802 of the stylus 800. The stylus 800 includes a stylus housing 804, astylus assembly 806, and a tip shield 808. The stylus housing 804, inone embodiment, is an elongated tube configured to receive the stylusassembly 806 and engage or couple to the tip shield 808. The stylusassembly 806 supports the various components described above withreference to FIG. 2. In short, the stylus assembly 806 supports thestylus tip 810, force sensor 812, TX driver and PSoC (not shown here).

The force sensor 812 comprises an actuator 814, a deformable and/orcompressible conductive diaphragm 816, an insulating spacer 818, and aconductive contact plate 820. The stylus tip 810, when pressing againstan object, transfers the force of the contact to the actuator 814, whichin turn presses on the deformable, semi-conductive diaphragm 816. Theforce causes the diaphragm 816 to contact the conductive contact plate820, which is then detected by the controller or PSoC (not shown). Forcesensors will be described in greater detail below with reference toFIGS. 9a -10 e.

FIGS. 9a-9c illustrate exemplary embodiments of a force sensorcomprising a deformable actuator. FIG. 9a depicts a plunger 902 coupledwith the stylus tip 904 that is configured to slide in and out of thestylus housing 906 as a force is applied to the stylus tip 904. Adeformable actuator 908 is disposed between the plunger 902 and a sensorsubstrate 910. The deformable actuator 908 biases the stylus tip 904 andcauses the stylus tip 904 to return to a fully extended position oncethe force is removed from the stylus tip 904. Stated differently, thedeformable actuator functions in a manner similar to a spring to returnthe stylus tip 904 to a default position.

FIG. 9b illustrates another embodiment of a force sensor utilizing adeformable actuator. The deformable actuator 912, in one embodiment,extends from the stylus tip 904 to the sensor substrate 910. Thedeformable actuator 912 may be over-molded onto a member 914 extendingfrom the stylus tip 904.

FIG. 9c illustrates one embodiment of a deformable actuator 916 directlyin contact with both the stylus tip 904 and sensor substrate 910. Inthis example, the stylus tip 904 moves up and down in the stylus housingand presses directly onto the deformable actuator when subject tovertical pressure.

FIG. 9d is an illustration of the operation of a deformable partiallyconductive actuator 918. As a force is applied to the stylus tip, andsubsequently transferred to the deformable actuator 918, the deformableactuator 918 deforms and the conductive surface of the deformableactuator 918 increasingly contacts a greater portion of a sensor 920.The sensor 920, in one example, includes a resistive trace across anactuator engaging surface of the sensor 920. As such, as the surface ofthe deformable actuator 918 that contacts the sensor 920 increases, theresistance of the resistive trace decreases. In other words, thedeformable actuator 918 increasingly shorts out more and more of theresistive trace as pressure is increased. Alternatively, the traces onthe surface of the sensor 920 may form an open circuit that is onlycompleted with a sufficient force on the deformable actuator 918. Inanother example, a ridge or other physical feature or mechanicalobstruction may be placed in the interior of the stylus housing suchthat the deformable actuator is maintained slightly out of contact withthe sensor 920 until a threshold amount of pressure exerted on thestylus tip overcomes the mechanical obstruction.

FIGS. 9e and 9f illustrate alternative substrate sensors for use withthe deformable actuator. Referring first to FIG. 9e , a non-conductivedeformable actuator 922 may be used with an optical sensor 924. Thedeformation of the actuator 922 is sensed optically. Light is directedinto the stylus housing between the deformable actuator 922 and thesensor 924 from an aperture in the substrate using a light source 926such as an LED. The sensor 924 is, in one embodiment, a photodiodeconfigured to sense light from the light source. As the actuator 922deforms, the aperture above the sensor 924 progressively closes,reducing the light incident on the sensor 924. In a further embodiment,a transparent disk may be placed above the substrate to prevent theactuator 922 from being pressed into the apertures in the substrate.

Examples of sensors 924 include, but are not limited to, photodiodes,phototransistors and light-sensitive resistors. The output of the sensor924 may be an analog signal which may vary in response to the forceexerted on the deformable actuator 922. Alternatively, a photo detectorarray such as a linear photodiode array may be used to improve accuracy.

FIG. 9f illustrates a capacitive sensor 928. A capacitor is formedbetween the surface of a carbon-imprinted actuator 930 and a circularPCB trace formed on an upper surface of the substrate 932, with thesolder resist 934 providing the dielectric. A hole in the PCB trace andsolder resist 934 allows an electrical contact to be made from the lowerside of the substrate 932 to the actuator 930.

As force is applied to the actuator 930, the actuator 930 deforms aspreviously described, causing the area of the upper plate of thecapacitor to increase, and thereby increase the total capacitancebetween the actuator 930 and the circular plate on the substrate 932.This capacitance may then be measured using one of the techniquespreviously described or other methods known to those skilled in the art.

Embodiments of the present invention, described herein, include variousoperations. These operations may be performed by hardware components,software, firmware, or a combination thereof. As used herein, the term“coupled to” may mean coupled directly or indirectly through one or moreintervening components. Any of the signals provided over various busesdescribed herein may be time multiplexed with other signals and providedover one or more common buses. Additionally, the interconnection betweencircuit components or blocks may be shown as buses or as single signallines. Each of the buses may alternatively be one or more single signallines and each of the single signal lines may alternatively be buses.

Certain embodiments may be implemented as a computer program productthat may include instructions stored on a computer-readable medium.These instructions may be used to program a general-purpose orspecial-purpose processor to perform the described operations. Acomputer-readable medium includes any mechanism for storing ortransmitting information in a form (e.g., software, processingapplication) readable by a machine (e.g., a computer). Thecomputer-readable storage medium may include, but is not limited to,magnetic storage medium (e.g., floppy diskette); optical storage medium(e.g., CD-ROM);

-   -   magneto-optical storage medium; read-only memory (ROM);        random-access memory (RAM); erasable programmable memory (e.g.,        EPROM and EEPROM); flash memory, or another type of medium        suitable for storing electronic instructions. The        computer-readable transmission medium includes, but is not        limited to, electrical, optical, acoustical, or other form of        propagated signal (e.g., carrier waves, infrared signals,        digital signals, or the like), or another type of medium        suitable for transmitting electronic instructions.

Additionally, some embodiments may be practiced in distributed computingenvironments where the computer-readable medium is stored on and/orexecuted by more than one computer system. In addition, the informationtransferred between computer systems may either be pulled or pushedacross the transmission medium connecting the computer systems.

Although the operations of the method(s) herein are shown and describedin a particular order, the order of the operations of each method may bealtered so that certain operations may be performed in an inverse orderor so that certain operations may be performed, at least in part,concurrently with other operations. In another embodiment, instructionsor sub-operations of distinct operations may be in an intermittentand/or alternating manner.

In the foregoing specification, the invention has been described withreference to specific exemplary embodiments thereof. It will, however,be evident that various modifications and changes may be made theretowithout departing from the broader spirit and scope of the invention asset forth in the appended claims. The specification and drawings are,accordingly, to be regarded in an illustrative sense rather than arestrictive sense.

The invention claimed is:
 1. An elongated stylus configured to becapacitively coupled with a sensor array that provides a plurality ofelectrodes and is controlled by a sensor controller, to indicate aposition on the sensor array, the stylus comprising: a housing having anend in an elongated direction of the housing; a first electrode disposedto at least partially extend from the end of the housing; a secondelectrode disposed around the first electrode; a signal transmit drivecircuit configured to transmit a stylus signal to the sensor array; anda stylus controller configured to control transmission of the stylussignal to the sensor array via at least one of the first electrode andthe second electrode; wherein the stylus controller is configured tosynchronize the transmission of the stylus signal to the sensor arrayvia the first electrode with a sensor signal transmitted from the sensorcontroller wirelessly and configured to electrically control the secondelectrode disposed around the first electrode to transmit the stylussignal to the sensor array via the second electrode while thetransmission of the stylus signal to the sensor array via the firstelectrode is not performed.
 2. The elongated stylus of claim 1, whereinthe stylus controller is configured to synchronize the transmission ofthe stylus signal to the sensor array with the sensor signal, using asynchronization signal received via an antenna inside the stylus.
 3. Theelongated stylus of claim 1, wherein the stylus controller is configuredto synchronize the transmission of the stylus signal with asynchronization signal transmitted from the sensor controller.
 4. Theelongated stylus of claim 1, wherein the stylus controller is configuredto synchronize the transmission of the stylus signal with a timing datasignal transmitted from the sensor controller.
 5. The elongated stylusof claim 1, wherein the stylus signal is modulated and differentiatedfrom the sensor signal that is code modulated.
 6. The elongated stylusof claim 1, wherein the stylus signal is phase modulated, frequencymodulated, amplitude modulated, or code modulated.
 7. The elongatedstylus of claim 1, wherein the stylus controller is configured tocontrol the second electrode disposed around the first electrode totransmit the stylus signal to the sensor array.
 8. The elongated stylusof claim 2, wherein the stylus controller is configured to control thesecond electrode disposed around the first electrode to selectivelytransmit the stylus signal via the second electrode and the firstelectrode.
 9. The elongated stylus of claim 3, wherein the styluscontroller is configured to control the second electrode disposed aroundthe first electrode to selectively transmit the stylus signal via thesecond electrode and the first electrode in synchronization with thesensor signal transmitted from the sensor controller.
 10. A capacitiveposition detection system comprising: (i) an active stylus configured tobe capacitively coupled with a sensor array to indicate a position onthe sensor array, the active stylus comprising: a housing having an endin an elongated direction of the housing; a first electrode disposed toat least partially extend from the end of the housing; a secondelectrode disposed around the first electrode; a signal transmit drivecircuit configured to transmit a stylus signal to the sensor array; anda stylus controller configured to control transmission of the stylussignal to the sensor array via at least the first electrode andconfigured to electrically control the second electrode disposed aroundthe first electrode to transmit the stylus signal to the sensor arrayvia the second electrode while the transmission of the stylus signal tothe sensor array via the first electrode is not performed; and (ii) thesensor array including a first set of conductors disposed in a firstdirection and a second set of conductors disposed in a second directiondifferent from the first direction, controlled by a sensor controller,wherein a finger and the active stylus are detectable on the sensorarray based on transmission signals supplied to the first set ofconductors and reception signals received in the second set ofconductors and based on stylus signals transmitted from the activestylus and received in the first and second sets of conductors, whereinthe sensor controller is configured to transmit a sensor signal to theactive stylus wirelessly to enable the stylus controller to synchronizethe transmission of the stylus signal via the first electrode of theactive stylus to the sensor array.
 11. The capacitive position detectionsystem of claim 10, wherein the stylus controller is configured tosynchronize the transmission of the stylus signal to the sensor arraywith the sensor signal, using a synchronization signal received via anantenna inside the stylus.
 12. The capacitive position detection systemof claim 10, wherein the stylus signal is modulated and differentiatedfrom the sensor signal that is code modulated.
 13. The capacitiveposition detection system of claim 10, wherein the sensor controller isconfigured to transmit the sensor signal by supplying the transmissionsignals to the first set of conductors.
 14. The capacitive positiondetection system of claim 10, wherein the stylus signal is phasemodulated, frequency modulated, amplitude modulated, or code modulated.15. The capacitive position detection system of claim 10, wherein thestylus controller is configured to control the second electrode disposedaround the first electrode to transmit the stylus signal to the sensorarray.
 16. The capacitive position detection system of claim 15, whereinthe stylus controller is configured to control the second electrodedisposed around the first electrode to selectively transmit the stylussignal via the second electrode and the first electrode.